This invention relates to a pilot valve for a control valve in a main flow line, and more particularly to such a pilot valve and method of operation utilizing a fluid source separate from the process fluid in the main flow line.
Heretofore, it has been common to utilize only the process fluid in the main flow line being sensed for the operation of the pilot valve for the main control valve. Oftentimes, the process fluid in the main flow line contains foreign matter which may clog or restrict flow passages, and bind or space opposed sealing and sliding surfaces. While pilot valves may be successfully used in such applications, an adequate maintenance and cleaning of the pilot valve is required in order to ensure that the pilot valve is fully functional. Continuous and frequent maintenance of such pilot valves is an undesirable feature.